The present invention relates to the formation of a tie-on thread of defined length at the bobbin of a textile machine in a procedure in which, after severing of the yarn at a point between the full bobbin and a yarn supply device, the yarn which is continuously supplied by that device is removed by means of a suction device and brought into engagement with a catch element which carries along the yarn in the direction of rotation of the bobbin and thus initiates the winding of both a yarn reserve and the principal winding on the bobbin.
This operation is carried out in an apparatus which includes a bobbin holder provided with two bobbin arms between which a bobbin can be held via rotatably mounted bobbin discs, one of the discs being provided with a catch element at its periphery, the apparatus further including a yarn supply device associated with the bobbin holder and a suction device including a suction tube and a collecting vessel.
In a known winding device for producing cylindrical yarn bodies in textile machines, the yarn which continues to be supplied after removal of a full bobbin is manually introduced into a suction device and during insertion of the empty bobbin and its contact with the slotted drum that drives it, a guide element is moved into an outer end position in the direction toward one of the bobbin arms to thus bring it into engagement with a catch hook which rotates together with the bobbin disc adjacent the guide element.
Upon severing of the yarn in communication with the suction device and winding of a transitional end piece onto an end region of the bobbin, the guide element is returned to its starting position so that the normal winding process can begin.
One drawback of this known apparatus is that the tie-on thread which is formed has an arbitrarily variable length. Tie-on threads which are too long in many cases cause difficulties during connection with a subsequent bobbin and, under certain circumstances, require additional process steps to shorten the tie-on thread, which at the same time involve greater yarn losses.
Moreover, there are a known process and apparatus for exchanging full bobbins for empty bobbins in textile machines, in which the end of the yarn which continues to be furnished by a yarn supply device is introduced substantially at the removal speed into the interior of the empty bobbin and the latter, before it is clamped into the machine, is preliminarily driven at the bobbin speed, and the yarn is held by being guided above the bobbin edge to be caught by the bobbin and wound onto the empty bobbin.
One embodiment of the apparatus for practicing this method is provided with an S-shaped subatmospheric pressure tube which can be pivoted between two end positions and which carries along the yarn sucked thereinto when it is pivoted into the interior of the empty bobbin. In one end position of the subatmospheric pressure tube the yarn is caught by a notch in the edge of the bobbin so that severing of the yarn section disposed in the subatmospheric pressure tube produces a yarn reserve and thereafter the actual wound bobbin.
One drawback of this known process and apparatus is that upon completion of the winding process there is no loop-shaped tie-on thread of defined length available which would permit further use of the bobbin without difficulty.